The Master-Oscillator Power Amplifier (MOPA) laser architecture is useful in applications requiring both high output pulse power and tight control of optical beam quality and wavelength. In the MOPA configuration, a low-power seed laser generates a train of initial pulses, which are then amplified by amplified stimulated emission (ASE) in one or more laser amplifiers to generate the desired high-power output. The last amplification stage is commonly referred to as the power amplifier, with prior stages termed “pre-amplifiers.”
Fiber lasers are often used in MOPA configurations. In a fiber laser, the active gain medium is an optical fiber, which is doped with rare-earth ions, such as erbium (Er), ytterbium (Yb), or combinations of multiple elements. The gain medium is optically pumped, for example by radiation emitted by a semiconductor laser diode, which can be injected into the cladding of the doped fiber.